News Scan Briefs: Do Rain Forests Make Rain?

A Lower High-Water Mark
The maximum global sea-level rise from the collapse of the rapidly warming West Antarctic ice sheet may be 3.2 meters—not five meters or more as predicted in the past. The revision comes from a new model suggesting that only parts of the ice sheet will collapse—namely, those that are grounded below sea level or sloping downward. Areas of the sheet grounded above sea level or on upward-sloping bedrock would remain in place. The results, in the May 15 Science, say nothing about disappearing ice sheets elsewhere, however. Greenland, for instance, holds enough ice to raise sea levels by seven meters. —David Biello

Do Rain Forests Make Rain?
Long-standing assumption: rain forests are a consequence of heavy rainfall. New hypothesis: some forested regions may produce conditions that lead to heavy rainfall. This “biotic pump” model contends that a vast forest such as the Amazon draws in large amounts of water vapor. Evaporation and condensation of the acquired water lead to a local atmospheric pressure drop. That decrease causes rain and attracts more water vapor to the forest, in a continuous positive feedback loop. “This theory could explain why continental interiors with huge rain forests remain so moist,” says Wildlife Conservation Society researcher Douglas Sheil, who in an April Bioscience paper revived the biotic pump model, originally proposed in 2006 by Anastassia Makarieva and Victor Gorshkov, both at the Petersburg Nuclear Physics Institute in Russia. “It could also underline the dangers of widespread deforestation.” Though promising, the model needs more data regarding air circulation patterns and vegetation types to support it, Sheil notes. —Steve Mirsky

Ants: “I’m Not Dead Yet”
Ants are notoriously efficient undertakers, carrying off dead nestmates before the corpses can infect the colony with their pathogens. Some researchers had hypothesized that ants detected breakdown products in decomposing bodies, but a new study undermines that theory. Entomologists from the University of California, Riverside, found that Argentine ants could detect dead nestmates before decomposition could have taken hold. More telling, the team found that living ants produce two “I’m not dead yet” chemicals, called dolichodial and iridomyrmecin. The compounds curb necrophoresis, the removal of dead colony members by fellow workers. Both chemicals dissipate quickly after death, plummeting to below half strength in just 10 minutes, the researchers write in a paper published in the May 19 Proceedings of the National Academy of Sciences USA. —John Matson

Working on the Railroad
A single railroad crosstie may not impact the environment as much as it helps to keep rails together. But considering that millions are deteriorating around the world, the material chosen as a replacement can affect the amount of carbon dioxide (CO2) in the air. Wood crossties require harvesting a lot of CO2-absorbing trees, roughly 89,000 cubic meters of timber per million crossties; concrete versions increase greenhouse gas emissions because of the fuel consumption during their manufacture. Robert H. Crawford of the University of Melbourne in Australia concludes that making enough concrete ties to keep one kilometer of tracks aligned for 100 years generates the equivalent of 656 to 1,312 metric tons of CO2. That amount is about one-half to one-sixth the amount that timber ties contribute, because concrete versions last longer and timber releases CO2 as it decays. Track the findings in the June 1 Environmental Science & Technology. —Charles Q. Choi

Temptation Zone
An imaging study reveals how the brains of some dieters stay disciplined and others give in to cravings. Researchers at the California Institute of Technology asked volunteers trying to slim down to pick a food toward which they felt neutral in terms of health and taste (many chose yogurt). They next scanned the dieters’ brains as they chose between this reference item and either healthy snacks, such as apples, or junk foods, such as candy bars. The team linked a brain region, the ventromedial prefrontal cortex, with the desire for tasty items, regardless of how unhealthy they might be. A separate area, the dorsolateral prefrontal cortex, was associated with self-control; dieters who had strong signals in this region chose the healthier food even if they did not think it tasted better. The findings, in the May 1 Science, present new targets that could help treat not only obesity but also addiction, wasteful spending, and other matters dealing with desire and restraint. —Charles Q. Choi